Integrated circuit chip manufacturers fabricate semiconductor devices by sequentially applying patterned layers of usually not more than 1 .mu.m thick to semiconductor wafers. The device layers may comprise various semiconductor or insulating layers in addition to one or more of the following conductive layers: a thin metal film such as tungsten, aluminum, copper, or titanium; a thin polycrystalline silicon (polysilicon) layer doped with impurities; or other layers of metal silicides and metal nitrides. Process control and manufacturing tolerances usually apply to the semiconductor device fabrication processes. Deviations from specified target tolerances in excess of only a few percentage points may result in defective and rejected semiconductor chips.
Semiconductor device manufacturers can only discard rejected semiconductor chips, thus resulting in undesirable production process waste and increased device manufacturing costs. If it is possible, however, to closely monitor various process and wafer parameters in situ during or immediately after processing each individual wafer, equipment and process inputs may be properly adjusted to reduce process parameter spread. Thus, a need exists for a method and apparatus to accurately measure physical parameters of a semiconductor wafer in situ for semiconductor wafer processing control and prognosis/diagnosis applications.
Methods for applying polycrystalline, amorphous, and single-crystal layers on semiconductor wafers include processes known as chemical-vapor deposition (CVD), evaporation, and other physical-vapor deposition (PVD) techniques such as sputtering. These thin-film deposition processes usually take place in a vacuum-tight deposition chamber filled with reactive process gases using thermal, plasma, or photo activation to generate the necessary species for deposition of the desired material layers. To maintain deposition uniformity across an individual semiconductor wafer surface, as well as process repeatability from wafer to wafer during the fabrication of many wafers, it is important to know the surface reflectance and roughness of the metal (or other polycrystalline) films deposited on the wafers. This is because for a given polycrystalline metal film thickness and metal film purity, a well-defined domain of surface reflectance and roughness values can be predicted. In the event that surface reflectance and roughness values fall outside the expected range of values, then the fabrication process may not be proceeding as expected even though the desired metal film thickness may be achieved. Examples of problems that would result in metal film surface reflectance and roughness values differing from expected values for a given metal film thickness are several. For example, CVD, evaporation, and other PVD processes usually operate within vacuum tight chambers. If vacuum integrity is not maintained in the process chamber, contaminants from the atmosphere external to the processing reactor may enter the process chamber. In such event, oxidation of the metal film or oxygen incorporation into the metal film will occur during deposition. Oxidation of the metal film (or oxygen incorporation) can change surface reflectance and roughness values for a given metal film thickness. As another example, it is important in many fabrication processes to prevent back-side film deposition on the semiconductor. wafer. A measurement of surface reflectance of the semiconductor wafer back-side can indicate the presence or absence of metal or another material layer.
Therefore, there is a need for a non-invasive in-situ method and apparatus for measuring surface reflectance and roughness of semiconductor wafer in a device fabrication reactor.
There are no known low-cost and simple methods or apparatuses that use an in-situ non-invasive sensor for measurements of semiconductor surface reflectance and roughness to monitor the important physical parameters associated with the semiconductor wafer fabrication process. In particular, there is not presently an apparatus that can provide non-invasive in-situ post-process surface reflectance and scattering measurements for CVD metal films or other polycrystalline CVD and PVD films such as polycrystalline silicon. Moreover, although some sensor systems can provide surface reflectance measurements of semiconductor wafers, no known system can provide non-invasive in-situ reflectance and scattering measurements immediately following a CVD or other deposition processes. There does not exist a low-cost compact sensor that can fit easily within a semiconductor wafer processing reactor to provide non-invasive in-situ measurements of semiconductor wafer surface reflectance and scattering or roughness for wafer processing diagnosis and prognosis applications.
Thus, there is a need for a non-invasive sensor that can provide surface reflectance and scattering measurements of wafers with metal films, polycrystalline films, and in general other material layers.
There is a need for a non-invasive in-situ sensor for performing surface reflectance and scattering measurements of metal films and other material layers on a semiconductor wafer immediately after a deposition or an etch process.
There is yet a need for a low-cost compact sensor that can be configured to operate in situ within a semiconductor processing reactor to provide surface reflectance and roughness measurements. Moreover, there is a need for an inexpensive and compact system that can provide the above measurements for process control and diagnosis/prognosis applications.